Influence of cholestyramine on the pharmacokinetics of rosiglitazone and its metabolite, desmethylrosiglitazone, after oral and intravenous dosing of rosiglitazone: Impact on oral bioavailability, absorption, and metabolic disposition in rats

Abstract

The possible influence of the bile acid-sequestering agent cholestyramine (CSA), which is a basic co-medication in hypercholesterolemic patients, on the pharmacokinetics of rosiglitazone (RGL) and its circulating metabolite desmethylrosiglitazone (DMRGL) was investigated following a single oral and intravenous dose of RGL to Wistar rats. The pharmacokinetic parameters of RGL and DMRGL were evaluated following oral or intravenous administration of RGL to rats at 10 mg kg⁻¹ with and without pre-treatment (0.5 h before RGL administration) of CSA at 0.057, 0.115, 0.23 and 0.34 g kg⁻¹ doses. With an increase in CSA dose there was dose-dependent decrease in area under the curve (AUC)_(0−∞) and C_max with no change in T_max, K_el and t_1/2 values for both RGL and DMRGL following oral administration of RGL. The oral bioavailability of RGL was reduced by 19.9, 35.6, 53.8 and 72.0% in rats following pre-treatment with CSA at 0.057, 0.115, 0.230 and 0.340 g kg⁻¹, respectively. There was no change in the above-mentioned pharmacokinetic parameters for RGL and DMRGL in rats when RGL was given intravenously following pre-treatment with the above-mentioned oral doses of CSA. Another objective of the study was to determine the effect of staggered oral CSA dosing at 1, 2 and 4 h after oral RGL administration at 10 mg kg⁻¹. AUC_(0−∞) of RGL and DMRGL was reduced following CSA staggered administration at 1 h, whereas 2- and 4-h staggered dose administration of CSA had no effect on the AUC_(0−∞) of RGL and DMRGL. Irrespective of CSA staggered dose administration there was no change in other pharmacokinetic parameters, namely C_max, T_max, K_el and t_1/2. The apparent formation rate constant (K_f) of DMRGL was also calculated to show that only the absorption of RGL was affected, not the apparent formation rate of DMRGL. The authors also studied the in vitro adsorption of RGL (100, 250, 500 µg ml⁻¹) at various pH conditions (pH 2, 4 and 7) and different concentrations of CSA (15, 30, 60 and 120 mg ml⁻¹). The percentage binding of CSA was in the range 50–72% (at pH 2), 74–89% (at pH 4) and 97–100% (at pH 7). In conclusion, we carried out a systematic investigation demonstrating mechanistically the interaction potential of RGL when co-administered with CSA. The applicability of the metabolite data after intravenous and oral dosing and pH-based binding experiments further adds credence to the key findings.

• Rosiglitazone
• desmethylrosiglitazone
• cholestyramine
• adsorption
• pharmacokinetics
• drug interactions